The present invention relates to a non-volatile memory and a fabrication method thereof, and more particularly, to a resistor type non-volatile memory and a fabrication method thereof.
Memory devices are typically divided into volatile and non-volatile types. For volatile memory devices, such as DRAM or SRAM, a continuous power supply is required to store data. For non-volatile memory devices, such as ROM, data can be stored therein for long periods of time without power supply.
As mobile phones, digital cameras, personal digital assistants (PDAs), notebooks, and other portable electronic devices become more popular, non-volatile memory devices are widely applied thereto due to advantages of retaining stored data without requiring power supply and low energy consumption overall. Among non-volatile memory devices, flash memory is the mainstream nowadays. As the semiconductor technology improves, flash memory devices face challenges of high operating voltage and gate oxidethinning, causing the unsatisfactory retention time. Thus, many new non-volatile memories are developed to replace flash memories. Among various emerging non-volatile memories, resistive non-volatile memory provides advantages of high write and erase speeds, low operating voltage, long retention time, simple structure, low power consumption, small size, and low cost.
FIG. 1 is a schematic diagram of a conventional resistor type non-volatile memory 10, disposed on a substrate 12, comprising a dielectric layer 14, a bottom electrode 16, a resistor layer 18, and a top electrode 20. The bottom electrode 16 comprises a platinum film. The resistor layer 18 comprises a chromium (Cr) doped strontium titanate single crystal and provides reversible resistance switching.
FIG. 2 shows the relationship between a bias and leakage current of conventional non-volatile memory 10. As shown in FIG. 2, when the bias voltage applied on the resistive non-volatile memory 10 increases positively from 0 V, the leakage current increases along the curve C1. However, when the positive bias exceeds V1, the relationship between the bias and leakage current suddenly switches to the curve C2. At that time, leakage current reduces immediately. The relationship therebetween follows the curve C2, even if the bias is reduced again. Until a negative bias less than V2 is applied to the resistive non-volatile memory 10, the relationship between the bias and the leakage current switches back to the curve C1 along with a suddenly increased negatively leakage current, which means the resistance of the resistive non-volatile memory 10 is reduced. Because of the special characteristics of resistance switching, the resistive non-volatile memory can be used as a memory. For example, these two different resistances can be used to represent 0 and 1 respectively. When write or erase is required in the memory device, they can be easily implemented by applying proper voltage to the resistive non-volatile memory 10 to change resistance. In addition, data stored therein is retained without power supply.
However, according to the conventional method of fabricating a resistive non-volatile memory, the fabrication of the bottom electrode 16 still presents problems. For example, the platinum film used in the bottom electrode 16 is extremely expensive. Also, in the conventional method of fabricating the resistive layer 18, two methods are typically used. In one, a single crystal structure of SrTiO3 is formed with an orientation (100) and then undergoes flame fusion to form a Cr doped SrTiO3 single crystal. Alternatively, a pulse laser sputtering process is used to grow a Cr doped SrZrO3 film. However, the single crystal structure used in the previous method also has high cost. The latter one is not suitable to form a large area film. Thus, neither method can meet requirements of mass production.
Thus, a new resistive non-volatile memory structure and a fabrication method thereof are desirable.